1. Field of the Invention
The present invention relates to a process for the production of quaternary ammonium hydroxides. More particularly, it is concerned with a process for producing high purity quaternary ammonium hydroxides by electrolyzing quaternary ammonium hydrogencarbonates.
2. Description of the Prior Art
Quaternary ammonium hydroxides are widely used in the electronics and semiconductor industry, specifically as cleaners, etchants, developers, etc. for wafers in the production of integrated circuits (IC) and large scale integrations (LSI).
With a recent increase in the degree of integration in semiconductors, it has been increasingly demanded to increase the purity of chemicals for use in the production thereof.
Quaternary ammonium hydroxides are not an exception to the requirement for purity. Thus, in order to increase the purity of quaternary ammonium hydroxides, the starting materials for use in production thereof and a process for the production thereof have been investigated.
For electrolytic production of quaternary ammonium hydroxides, many methods have been proposed, including those as described in, for example, Japanese Patent Publication Nos. 28564/1970, 14885/1971, Japanese Patent Application Laid-Open Nos. 155390/1982, 181385/1982, 193287/1984, 193288/1984, 193228/1984, 100690/1985, 131985/1985 and 131986/1985.
In the above methods, as quaternary ammonium salts to be subjected to hydrolysis, quaternary ammonium halides, quaternary ammonium sulfates, etc. are mainly used. However, when quaternary ammonium halides are used, part of halogen ions pass through the cation exchange membrane and enter the cathode compartment, thereby contaminating the final product of quaternary ammnium hydroxides and, therefore, high purity quaternary ammonium hydroxides are difficult to produce. Furthermore, halogen gas is generated during the electrolysis, thereby causing problems such as corrosion of the anode itself. Since the halogen gas generated is harmful, it is necessary to install equipment for removal or neutralization of the halogen gas.
When quaternary ammonium sulfates are used as the starting material, problems arise in that they are difficult to handle, and sulfuric acid formed during the electrolysis corrodes the electrodes and equipment. Thus, high purity quaternary ammonium hydroxides are difficult to produce from quaternary ammonium sulfates.
When quaternary ammonium organic carboxylic acid salts as described in Japanese Patent Application Laid-Open No. 100690/1985 are used as the starting material, organic carboxylic acids are formed during the electrolysis, which may undesirably corrode the anode itself. Furthermore, part of the organic carboxylic acids may pass through the cation exchange membrane and intermingle with the final product of quaternary ammonium hydroxides, thereby decreasing the purity thereof.
Electrolysis of quaternary ammonium hydrogencarbonates using a diaphragm made of such materials as porcelain, carborundum and arandum is disclosed in Japanese Patent Publication Nos. 28564/1970 and 14885/1981. By the use of such a diaphragm, however, high purity quaternary ammonium hydroxides cannot be obtained, and the method has disadvantages in that the current efficiency is low.